23 August 2010

Our friend Bruce has shared another one of his vacuum tube projects with the DIY community. His latest project is the ForeWatt Tube Preamplifier which is an ECC802S (12AU7 / ECC82) tube preamplifier. The tube preamp uses a SRPP topology with ECC802S tube that can be substituted with 12AU7 and ECC82 tubes. The gain of the preamp can be set 7 (~17dB) or 11 (~21 dB). The lower gain setting is realized when the cathode bypass capacitor is omitted. Naturally a switch can be used to change gain if desired. Shown in the photo below is the Type I preamplifier build which uses a manual rotary switch for input selection and a manual Alps Blue Velvet potentiometer to attenuate the input signal. The fabulous wooden enclosure was built by fellow hobbyist Jeff.

The power supply is solid state and the DC is used to heat the tubes. In the Type II version of the preamplifier shown in the photo below a remote control module is used for signal selection and signal attenuation. With the remote control module the preamplifier can also be used as a passive (no gain) preamplifier.

Bruce reports that with the ForeWatt preamplifier there is very clean with plenty of detail, a wide soundstage and that typical warm lush tube sound. The measure performance of the preamp is very good.